A retainer and a cotter serve as a mechanism for mounting a spring in a compressed state along an outer periphery of a shaft member, and are applied to a valve shaft of an engine, etc. (for example, see Patent Literature 1). Specifically, a protrusion formed on an inner peripheral surface of the cotter is engaged with a recess (annular groove) formed in an outer peripheral surface of the shaft member in an axial direction. In this state, an outer peripheral surface of the cotter and an inner peripheral surface of the retainer are taper-fitted to each other, and the spring is locked by the retainer. Consequently, the spring is kept in the compressed state.
When assembling the retainer and the cotter to the shaft member as described above, it is difficult to perform such an operation that the cotter divided into a plurality of pieces is mounted at the outer periphery of the shaft member and the protrusion of the cotter is fitted into the recess of the shaft member. For that reason, various methods have been conventionally proposed for reliably assembling the retainer and the cotter to the shaft member. For example, Patent Literature 2 discloses the following method. Specifically, the shaft member is inserted from below the cotter, and the cotter is pressed from the outer periphery thereof under a state in which correspondence is established between an axial position of the protrusion of the cotter and an axial position of the recess of the shaft member. As a result, the cotter and the shaft member are fitted to each other. At this time, the retainer and a pressing member sandwich the cotter from both sides in the axial direction of the cotter, and hence the cotter is positioned at a predetermined position.